Snow and ice cause significant hardship in cold climates. Major issues from freezing conditions are the loss of normal friction on surfaces and the buildup of ice. The consequences range from personal slip and fall injuries to collisions on the roadways and to economic losses in conveying material. Especially, the airline sector combats winter conditions to keep runways open and to keep exposed aircraft components from freezing.
Road maintenance crews most often use granular sodium chloride, more commonly referred as “road salt” for deicing. The salt suppresses the freezing point of water and converts ice or snow to ionic solution. The road salt loses its effectiveness completely at below −18° C., which is the freezing point of a saturated sodium chloride solution. Road salt is corrosive to ferrous metals commonly found in the vehicles and structures. Significant economic loss can be attributed to maintenance of transportation infrastructure and reduced life of vehicles due to rusting.
Other inorganic salt replacements have been proposed and tested, including magnesium and calcium chloride. Although some corrosion aspects are avoided, the inorganic salts tend to leave a solid residue on surfaces. Also, surface water and ground water salination are possible results from overuse of the inorganic salts.
Organic deicers, which leave no residue, are used for deicing and anti-icing applications in aircraft as well as vehicles. Common examples of such deicers include ethylene glycol and methanol, which both exhibit toxicity towards human and aquatic life.
Organic salt deicers have gained acceptance in the corrosion-averse applications such airport runway deicing. In the past 20 years, organic salts have replaced urea as the deicer of the choice. Urea is a nitrogen-based chemical, which promotes plant growth. Potassium/sodium acetate is more expensive than sodium chloride. Because of the low corrosiveness of potassium/sodium acetate, the most common use is for airport runway deicers. Recently, they replaced urea as a more environmentally friendly medium. Acetates are biodegradable and do not provide nutrients into surrounding streams and groundwater.
In 2009, U.S. Environmental Agency proposed rule 40 CFR Part 449 (44684 Federal Register/Vol. 74, No. 166/Friday, Aug. 28, 2009); Effluent Limitation Guidelines and New Source Performance Standards for the Airport Deicing Category. This rule requires large airports performing airfield pavement deicing to use non-urea-based deicers. Based on a 2009 survey of 325 primary airports, the U.S. EPA estimates that most common deicing chemicals are potassium acetate (63 percent); urea (12 percent); propylene glycol-based fluids (11 percent); sodium acetate (9 percent); sodium formate (3 percent); and ethylene glycol-based fluids (2 percent).
North American acetate-based runway deicers are covered in FAA-approved specification SAE AMS 1435A. Because over 90% acetic acid is produced starting from fossil fuel derived sources, the acetate based deicers have a large carbon footprint. U.S. manufacturers include of acetate based deicers include Cryotech Inc.
Potassium formate is commonly used for deicers in European airports. The biological oxygen demand from formate is lower than from acetate. The potassium formate deicer is covered in FAA-approved specification SAE AMS-1431B. Formic acid may be produced as an acetic acid byproduct or by direct synthesis with carbon monoxide and alcohol. European manufacturers of potassium formate-based deicers include Kemira Inc.
One concern in organic salt-based deicers is the oxidation of brake pads in the aircraft. Therefore, corrosion inhibitors are to be added to the formulations. Potassium formate is currently not recommended in the U.S. because of corrosion concern (FAA CERT ALERT NO. 01-04, 19 Dec. 2001).
New green deicer alternatives from biobased sources include propanediol and glycerin byproduct from biofuel production to address corrosiveness and carbon footprint. These were used also to alleviate potassium acetate shortage in the 2009/2010 season, because of a mining strike in Canada.
Peel (U.S. Pat. No. 4,746,449) teaches deicing products obtained from pulp mill black liquor consisting of acetates, formates, and lactates in certain ratios. The cations include calcium, magnesium, sodium and ammonia.
Stankowiak, et al. (U.S. Pat. No. 6,059,989) teach a deicing composition based on acetates and/or formates, and a method for melting snow and ice on traffic areas with the aid of said composition. Stankowiak, et al. list silicate and phosphate as active ingredients.
Improved deicers are needed in the market. What are needed are deicer compositions that mitigate corrosion concerns and have a good environmental lifecycle (such as being produced from biomass), while performing as good as incumbent deicers.